Uplink Time Difference of Arrival (UTDOA) is a positioning method based on time of arrival techniques. Such techniques are described in the 3GPP specifications 3GPP RP-040387, WID: Inclusion of Uplink TDOA UE positioning method in the UTRAN specifications and 3GPP R4-040412, Inclusion of Uplink TDOA UE positioning method in the UTRAN specifications; TruePosition.
In the UTDOA positioning method, Location Measurement Units (LMU), usually associated with radio base stations measure the time of arrival of UE transmitted signals and the UE location can be computed when at least three LMUs are able to detect the UE signal. Signal detection is normally done by correlating the received signal against a known signal replica for all possible delays and doppler shifts. This is in practice done by using discrete steps, also referred to as “bins”, in the delay and doppler domain.
Furthermore, correlations are normally done in two steps. First, coherent correlation is done (i.e. using both inphase and quadrature components) in order to optimally suppress noise. Subsequently, different segments of coherent correlation results can be added non-coherently, ie the individual coherent correlation results are absolute-squared, followed by a summation. Non-coherent correlation may e.g. become necessary whenever the signal phase changes too much between two coherent correlation segments. Once the correct delay/doppler bin has been identified, a finer search may be done in order to increase the accuracy.
According to the current standard as described in the above cited 3GPP specifications, it is assumed that coherent correlation is done during the whole signal duration. For a stationary UE, this provides the best sensitivity for a given measurement interval. However, when UE acceleration is taken into account the maximum coherent correlation time is limited by the change in doppler during the measurement interval. Therefore it would be desirable to achieve a method and arrangement for detecting a signal for the scenario when the UE accelerates.
Thus, the object of the present invention is to improve sensitivity and to avoid unnecessary processing during an acceleration of the UE.